Warm Autoimmune Hemolytic Anemia as a Rare Presentation of Pre-fibrotic Primary Myelofibrosis.

Primary myelofibrosis (PMF) is an uncommon chronic myeloproliferative disorder that is commonly associated with Janus kinase 2 (JAK-2), calreticulin (CALR), or thrombopoietin receptor (MPL) mutations. Pre-fibrotic PMF (also known as pre-PMF or early PMF) is a subtype of PMF that is defined by a lower grade of fibrosis. In this report, we present a rare case of warm autoimmune hemolytic anemia (wAIHA) associated with pre-PMF. The patient is a 64-year-old female with chronic thrombocytosis who presented with wAIHA. She underwent treatment with high-dose steroids and intravenous immunoglobulin which was unsuccessful. Subsequent treatment with rituximab successfully caused her wAIHA to go into complete remission, without the need for maintenance therapy. A bone marrow biopsy showed pre-PMF. Her warm autoimmune hemolytic anemia was thought to be related to cytokine dysregulation and autoantibody formation, which is commonly seen in pre-PMF. Underlying myelofibrosis should be considered in a patient who presents with wAIHA and other hematologic abnormalities. In such cases, a bone marrow biopsy should be performed as part of the workup. Further investigation is required to determine the mechanism behind this association.